Outdoor navigation is widely deployed thanks to the development of various global-navigation-satellite-systems (GNSS), e.g., Global Positioning System (GPS), GALILEO, and the like.
Recently, there has been a lot of focus on indoor navigation. This field differs from the outdoor navigation, since the indoor environment does not enable the reception of signals from GNSS satellites. As a result, a lot of effort is being directed towards solving the indoor navigation problem.